Natural killer cell function results from the balance of expression of inhibitory and activating receptors at the plasma membrane. This unit of the program will define membrane traffic pathways involved in post-translational control of NK cell receptor expression in order to determine how regulation of these pathways can influence NK cell function. There has only been limited analysis of endocytic pathways of NK receptors and no NK receptors have been analyzed for their biosynthetic pathways. The studies in this unit redress these deficits of information with the goals of comparing endocytic and biosynthetic regulation of activating and inhibitory KIRs, as well as defining chaperone pathways that influence KIR folding and stability. In addition, membrane traffic pathways regulating NK cell-target cell interactions at the synapse will be defined. The specific aims are as follows. Aim 1 is to characterize the endocytic behavior of inhibitory (KIR2DL1) and activating (KIR2DS1) NK receptors to test the hypothesis that surface activity of each class of receptor is regulated by different responses to ligand. The role of CDS signaling in KIR endocytosis will also be assessed. Aim 2 is to test the hypothesis that polymorphism of the KIR3DL1 locus can influence receptor expression at the NK cell plasma membrane by affecting membrane traffic behavior in the biosynthetic pathway and to compare the biosynthetic pathways of inhibitory and activating KIR. These studies will establish the chaperone pathways that influence levels of KIR receptor expression and that are susceptible to polymorphic variation of the receptors, as well as to stress effects during infection. Aim 3 is to test the hypothesis that clathrin-mediated membrane traffic at the NK cell-target synapse is required for functional killer-target interactions. The involvement of clathrin in ligand trans-endocytosis by NK cells and in cytotoxicity of target cells will be analyzed using techniques that inhibit clathrin expression. Definition of receptor trafficking pathways by the studies proposed for this unit of the program makes it possible to understand how receptor polymorphisms and the signaling pathways of NK receptors could influence the relative receptor expression levels that are critical for determining individual NK cell activity. This information is needed to appreciate the functional interplay of NK cell populations operating during HIV infection.